The invention relates to a process for decreasing the permeability of a permeable subterranean earth formation. More particularly, it relates to plugging pores located within the first few inches of the portion of an earth formation that is encountered by the bore hole of a well, and provides a means for doing so in earth formations that are relatively highly permeable and/or fractured.
The positioning of a plugging material within the first few inches of an earth formation is particularly valuable for use in the injectivity profile improving process of the copending patent application by J. H. Thommer, Ser. No. 362,624, filed May 21, 1973, now U.S. Pat. No. 3,830,299. In that process, variation with depth in the fluid flow pattern of a well is determined, the first few inches of all permeable portions of the surrounding earth formations are plugged, and then at least some of the plugged portions are perforated with openings that are sized and located to provide selected rates of flow at selected depths.
Both the utility of plugging a subterranean earth formation and various ways of doing it with an asphalt emulsion were previously known. In 1933 the application for U.S. Pat. No. 2,201,459 described the use of aqueous dispersions of asphalt in an aqueous liquid which contained an acid soap-type emulsifying agent and a pH reducing reactant, such as methyl formate to cause the emulsion to break. The T. K. Miles U.S. Pat. No. 2,378,235 describes the relatively incomplete breaking of such emulsions and a procedure for improving that problem, by dissolving a cationic surfactant in the asphalt so that it migrates to the surface of the droplets and subsequently causes their coagulation. U.S. Pat. No. 3,026,266 describes asphalt emulsions in which the tendency of the asphalt to stick to siliceous materials is improved by using cationic surfactants as emulsifiers and polyamide condensation products of polymerized acids and polyamines as modifiers. U.S. Pat. No. 3,159,976 describes an earth formation plugging process for avoiding the slow breaking tendancy of such cationic asphalt emulsions, by separately injecting the emulsion and a strong base to mix in or near the zone to be treated and cause a quick coalescence of the asphalt particles. The H. J. Sommer and W. C. Simpson U.S. Pat. No. 3,324,041 describes a polyepoxide-containing asphalt emulsion in which emulsions of both a polyepoxide and a nonionic surfactant are mixed to form a composition which is subsequently solidified by an interaction of the polyamide and the polyepoxide.